An alkaline zinc battery consists of at least one positive electrode, at least one negative zinc electrode, separators to keep the electrodes from touching each other and a cell case and connectors. Ideally, the zinc electrode should be made of zinc but the fabrication of a suitable electrode made of zinc has up until now not been successful. Zinc electrodes are presently mainly made of zinc oxide and additives applied to a substrate or grid. The battery has an energy density higher than, but a cycle life shorter than a lead-acid battery.
There are two reasons for the short cycle life. When zinc metal is converted to zinc oxide in an alkaline electrolyte during discharging, the zinc oxide dissolves into the electrolyte until the solution is saturated. When the cell is being recharged, that dissolved zinc oxide is plated out of solution in the form of metallic zinc. When zinc is plated out of an alkaline electrolyte, "dendrites" form. The dendrites will eventually penetrate the separators and cause a short-circuit that causes the cell to discharge at a high current. Eventually, the cell will no longer be able to be recharged or even sustain an open circuit voltage.
Dendrites tend to form predominantly during charging of the battery, and especially during the overcharge portion of the charge cycle. The formation of dendrites is avoided to some extent by special charging techniques and by maintaining an excess of zinc oxide in the zinc electrode.
The second reason for the short cycle life is that zinc electrodes are made by applying some composition of zinc, zinc oxide and certain additives to a suitable current collector. The current collector may be made of a metal such as copper. The zinc metal and/or zinc oxide particles are usually held together and to the current collector by some polymer material. During cycling, the active material of the zinc electrode tends to shift towards the bottom and bottom center of the electrode. This not only reduces the surface area of the active portion of the electrode, but also leads to the formation of dendrites because the current (especially when charging) becomes concentrated on a smaller area.